Electronic article security (EAS) systems for detecting and preventing theft or unauthorized removal of articles or goods from retail establishments and/or other facilities, such as libraries, have become widespread. In general, such security systems employ a security tag which is secured to or associated with an article (or its packaging), typically an article which is readily accessible to potential customers or facility users and, therefore, is susceptible to unauthorized removal. In general, such EAS systems are employed for detecting the presence (or the absence) of a security tag and, thus, a protected article within a surveilled security area or detection zone. In most cases, the detection zone is located at or around an exit or entrance to the facility or a portion of the facility.
One type of EAS system which has gained widespread popularity utilizes a security tag which includes a self-contained, passive resonant circuit in the form of a small, generally planar printed circuit which resonates at a predetermined detection frequency within a detection frequency range. A transmitter, which is also tuned to the detection frequency, is employed for transmitting electromagnetic energy or an interrogation signal into the detection zone. A receiver, tuned to the detection frequency, is positioned proximate to the detection zone. Typically, the transmitter and a transmitter antenna are located on one side of an exit or aisle and the receiver and a receiver antenna are located on the other side of the exit or aisle, so that a person must pass between the transmitter and receiver antennas in order to exit the facility. When an article having an attached security tag moves into or passes through the detection zone, the security tag is exposed to the transmitted energy (the security tag is interrogated), resulting in the resonant circuit of the tag resonating to provide an output signal detectable by the receiver. The detection of such an output signal by the receiver indicates the presence of an article with a security tag within the detection zone and the receiver activates an alarm to alert appropriate security or other personnel.
Existing EAS systems of the type described above and of other types have been shown to be effective in preventing the theft or unauthorized removal of articles.
Security tags of the type described used in a particular store or chain of stores are typically identical. Thus, all articles, regardless of size or value, which include the securi:y tag return an identical signal to the receiver. Recently, passive resonant security tags which return unique or semi-unique identification codes were developed. U.S. Pat. No. 5,446,447 (Carney et al.), U.S. Pat. No. 5,430,441 (Bickley et al.), and U.S. Pat. No. 5,347,263 (Carroll et al.) disclose three examples of such security tags. These security tags typically include an integrated circuit to generate the identification code. Such "intelligent" security tags provide additional information about the article detected in the zone of the interrogator.
When it is desired to deactivate a security tag, such as when a tagged article is purchased, the usual approach with the prior art EAS systems is to physically deactivate or physically disable the security tag so that the tag does not respond to an interrogation signal sent out by the interrogator or transmitter when the tag passes through the detection zone. One common technique for physically deactivating a security tag is to destroy some portion of the resonant circuit, such as a capacitor. Another technique involves covering the tag with a shield on either a permanent or temporary basis to prevent the tag from being exposed to an interrogation signal. A third technique involves surrounding a portion of the tag coil with a magnetizable and demagnetizable metallic element which, according to whether the element is magnetized or demagnetized, changes the tag Q so that it becomes either detectable or undetectable by an interrogator.
Despite the widespread use of such security tags, and, more recently, RFID tags, there is still a need to expand the functional capabilities of EAS and other systems which use RFID tags. Specifically, it would be desirable to create databases which interact with interrogators and RFID programming equipment to identify and track the status of individually tagged articles. It would also be desirable to "deactivate" RFID tags in a manner which allows the tags to be conveniently reactivated. It would also be desirable to deactivate and reactivate RFID tags in a manner which does not require physically or electronically altering the tag itself. The present invention addresses these needs by providing a method of using deactivatable and reactivatable RFID tags which are tracked by a database so that the status of the tagged article may be tracked throughout its life cycle.